Update docs and typespecs for lock_status, closes #7125

Author: José Valim

lib/mix/lib/mix/scm.ex

@@ -96,13 +96,13 @@ defmodule Mix.SCM do
 
   The lock is sent via `opts[:lock]` but it may not always be
   available. In such cases, if the SCM requires a lock, it must
-  return `:lockmismatch`, otherwise simply `:ok`.
+  return `:mismatch`, otherwise simply `:ok`.
 
   Note the lock may also belong to another SCM and as such, an
   structural check is required. A structural mismatch should always
   return `:outdated`.
   """
-  @callback lock_status(opts) :: :mismatch | :outdated | :nolock | :ok
+  @callback lock_status(opts) :: :mismatch | :outdated | :ok
 
   @doc """
   Receives two options and must return `true` if they refer to the